Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$70.40	10.840%	$78.0314	$78.03	$78.05	$78.00
Purchase #2	$125.87	13.473%	$142.8285	$142.83	$142.85	$142.80
Purchase #3	$10.99	12.710%	$12.3868	$12.39	$12.40	$12.40
Purchase #4	$214.88	5.345%	$226.3653	$226.37	$226.35	$226.40
Purchase #5	$69.67	12.498%	$78.3774	$78.38	$78.40	$78.40
Purchase #6	$101.25	8.478%	$109.834	$109.83	$109.85	$109.80
Purchase #7	$153.46	11.728%	$171.4578	$171.46	$171.45	$171.50
7 purchase totals =	$746.52		$819.2812	$819.29	$819.35	$819.30